The invention relates to a cooling apparatus for an electric motor control unit, and more particularly to a cooling apparatus suitable for cooling a module of an inverter, or the like, of an electric motor control unit integrated with a driving device for an electric vehicle or a driving device for a hybrid vehicle.
A driving device for a vehicle using an electric motor as a drive source employs a structure in which a control unit having a built-in inverter or the like for controlling the electric motor is integrated with the driving device, giving the driving device an advantage in terms of handling and installation space in a vehicle. When the electric motor control unit and the driving device are integrated as such, the electric motor control unit is exposed to heat from the electric motor of the driving device in addition to heat generated from the electric motor control unit itself. Furthermore, a device, such as a driving device for a hybrid vehicle, exposed to heat generated from a combustion engine is disposed directly to a heat sink provided with a coolant passage so as to cool a power module of the electric motor control unit in particular. Japanese Patent Laid-Open Publication No. 2001-119898 discloses such a conventional structure in which a coolant passage is defined in a heat sink. In this structure, a race with a bottom, that is a surface to which a module of an electric motor control unit is mounted in close contact, is formed in the heat sink. A partition plate is attached on an opening face side of the race and the coolant passage surrounded by the race and the partition plate is formed by bolting the partition plate to fix to the heat sink.
Meanwhile, coolant leakage to the module constituting an electric motor control unit, such as above, must be avoided by all means to ensure operation of a module electronic circuit. However, in the conventional method, the thickness between a bottom portion of a bolt hole and a module mounting surface is significantly reduced by forming the bolt hole in the heat sink, which is a cast made of aluminum or the like to ensure thermal conductivity. Therefore, if there are any cavities in this portion, the bottom portion of the bolt hole and the module mounting surface may be linked through the cavities during a screw-cutting process for the bolt hole, causing fluid of the coolant passage and fluid outside the partition plate to leak to the module mounting surface through the cavities. In particular, when a finish machining process is applied to the module mounting surface to improve thermal conductivity on the module mounting surface, cavities which were not linked before may be linked by the process.
In order to prevent such leakage through the cavities, there is a method of setting the module mounting surface, to which finish machining is applied, higher than an outer surface of the bottom portion of the bolt hole so that the outer surface of the bolt hole bottom portion remains unprocessed. When such an arrangement is employed, close contact between the outer surface of the bolt hole bottom portion and the module can no longer be expected, which reduces a contact area of the machined surface of the heat sink with respect to the module. Therefore, cooling capability is inevitably lowered. In addition, there is another method in which the thickness of the bolt hole bottom portion is increased. With this method, the thickness of the entire heat sink increases, resulting in size and weight increases, which are not preferable.
It is an object of the invention to provide a cooling apparatus for an electric motor control unit capable of preventing fluid leakage from a mounting portion of a component member of a coolant passage, without increasing a thickness of the heat sink or reducing the heat exchange area.
In order to achieve aforementioned object, according to the invention, a cooling apparatus for an electric motor control unit includes a heat sink contacting modules of an electric motor control unit, a concave portion continuously formed in the heat sink, and a wall member mounted on an opening face side of the concave portion so as to be fixed to the heat sink, which defines a coolant passage in the heat sink together with the concave portion of the heat sink, wherein the heat sink includes a projection projecting from a mounting surface with respect to the wall member; the wall member includes a hole fitted into the projection; and the wall member is fixed to the heat sink by press-fitting the projection of the heat sink.
Because this structure does not require forming a thin wall portion that exceeds the thickness of a bottom portion of a race in order to fix the wall member to the heat sink, connection in the thin wall portion through cavities can be prevented. Thus, with the structure, fluid leakage to the contact portion side of the module that is generated when fixing the wall member can be prevented without increasing the thickness of the heat sink or reducing a heat exchange area.
In the aforementioned structure, it is effective to employ a structure in which the concave portion is a race that winds so as to substantially extend over an entire area of the heat sink.
Because this structure does not require providing a space for arranging a bolt hole requiring a constant thickness therearound between the races of the heat sink, the heat exchange area can be increased by densely arranging the races, thus improving the cooling efficiency of the heat sink.
In the aforementioned structure, it is effective to employ a structure in which a dividing wall, the height of which, from a bottom of the race, is shorter than a depth of the race, is provided along the race.
In this structure, the dividing wall provided along the race functions as a fin for increasing the heat exchange area and as a guide for uniformly providing a flow rate of the coolant in a race width direction, thus further improving the cooling efficiency of the heat sink.
In the aforementioned structure, it is even more effective to employ a structure in which the concave portion is structured from a space between a plurality of pin-like fins rising from a bottom portion of the heat sink.
In this structure, because a heat exchange portion contacting the coolant passage is comprised of pin-like fins with low resistance, a pressure difference at each portion in the passage becomes small. Thus, even if a flow amount of the coolant is increased, it is possible to reduce the amount of fluid leaking from the passage as the generation of a partial high-pressure portion is inhibited. In addition, the structure of the coolant passage is simplified.
In the case of the aforementioned structure, it is even more effective to employ a structure in which the plurality of pin-like fins are evenly arranged on substantially the entire surface of the heat sink.
In this structure, a pressure loss generated by the pin-like fins across the entire coolant passage is substantially uniform. Accordingly, with this structure, even if the flow amount of the coolant is increased, it is possible to further reduce the amount of fluid leaking from the passage as the partial high-pressure portion is not generated. In addition, the structure of the coolant passage can be further simplified, thus achieving an uniform cooling efficiency over the entire heat sink.
Further, the aforementioned structure can be structured such that a part of the plurality of pin-like fins have the projections at the tips thereof.
In this structure, the pin-like fins can be used as a fixing mechanism of the wall member with respect to the heat sink.
It is effective to apply each of the aforementioned structures to a structure in which a contact surface of the heat sink with the modules is a surface to which finish machining is applied.
In this structure, it is not necessary to consider the connection through cavities generated by applying the finish machining process to the thin wall portion. Therefore, the cooling efficiency can be improved by applying finish machining to the contact surface between the heat sink and the module so as to being the heat sink in closer contact with the module.
It is even more effective to apply each of the aforementioned structures to a structure in which the heat sink is fixed on a driving device case of a driving device for a vehicle, including an electric motor, at a predetermined distance to define a return passage for a coolant between the driving device case and the wall member of the heat sink.
In this structure, the coolant flowing in the heat sink used for cooling the module can be used to cool the driving device case side. In addition, because the outer side of the wall member constitutes a passage for the coolant, a special sealing mechanism for completely preventing the leakage of the coolant from the passage in the heat sink to the outer side of the wall member is not required.